Enhancement/mcp apps by MarcSkovMadsen · Pull Request #161 · MarcSkovMadsen/holoviz-mcp

MarcSkovMadsen · 2026-03-06T18:20:54Z

No description provided.

…into enhancement/mcp-apps

Copilot

Pull request overview

Adds MCP App-compatible rendering for visualization tools, including a new show_pyodide flow for browser/Pyodide execution, plus URL externalization support for proxied/Codespaces environments.

Changes:

Introduces MCP App resources/templates for show and show_pyodide, and returns structured JSON payloads for app rendering.
Extends the display system to accept a pyodide execution method and improves URL generation for Jupyter proxy/Codespaces.
Adds/updates tests and documentation to cover the new tool behavior and configuration.

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
tests/test_server.py	Asserts `show_pyodide` is registered on the composed server.
tests/docs_mcp/test_docs_mcp.py	Adds contract tests for `show` JSON payloads, `show_pyodide` payloads, and URL rewriting behavior.
tests/display_mcp/test_endpoints.py	New endpoint tests for method handling and proxy/Codespaces URL formation.
tests/display_mcp/test_database.py	Tests database acceptance/validation of the `pyodide` method.
tests/config/test_loader.py	Verifies `display` config is preserved and can be overridden by user config.
src/holoviz_mcp/holoviz_mcp/templates/show_pyodide.html	Adds an MCP App UI for rendering tool payloads via panel-live/Pyodide.
src/holoviz_mcp/holoviz_mcp/templates/show.html	Adds an MCP App UI for rendering `show` results (JSON + legacy text fallback).
src/holoviz_mcp/holoviz_mcp/server.py	Adds App resources, URL externalization helper, and JSON payload output for `show` / new `show_pyodide` tool.
src/holoviz_mcp/display_mcp/pages/view_page.py	Prepends Panel reset code before executing snippets.
src/holoviz_mcp/display_mcp/endpoints.py	Centralizes external base URL derivation (proxy/Codespaces/config).
src/holoviz_mcp/display_mcp/database.py	Adds `pyodide` to supported methods and validates method values.
src/holoviz_mcp/config/loader.py	Adds default `display` config and ensures it isn’t filtered out.
docs/explanation/tools.md	Documents `show` / `show_pyodide` tools.
docs/explanation/display-system.md	Updates architecture explanation to include `show_pyodide` and `pyodide` method.
.vscode/settings.json	Removes an unused VS Code setting entry.

Comments suppressed due to low confidence (1)

src/holoviz_mcp/holoviz_mcp/server.py:521

show() now forwards method through to the display server and the rest of the PR adds support for pyodide, but this tool’s type hints/docs still restrict method to only "jupyter" | "panel". This makes the public MCP API inconsistent with both the docs and the display server behavior; update the Literal[...] (and the docstring section that enumerates methods) to include "pyodide" or remove the Literal if you want to allow future methods without churn.

    code: str,
    name: str = "",
    description: str = "",
    method: Literal["jupyter", "panel"] = "jupyter",
    ctx: Context | None = None,

Copilot · 2026-03-06T18:27:17Z

@@ -150,7 +161,7 @@ def _execute_code(snippet: Snippet) -> pn.viewable.Viewable | None:
    else:  # panel method
        # Execute code that should call .servable()
        execute_in_module(
-            snippet.app,
+            app,
            module_name=module_name,
            cleanup=True,  # Can cleanup immediately
        )


Snippet.method now allows "pyodide", but _execute_code() treats any non-"jupyter" method as the Panel execution path, so pyodide snippets would be executed server-side and expected to call .servable(). This contradicts the intent of the pyodide method and can lead to confusing failures. Add an explicit elif snippet.method == "pyodide" branch (e.g., render a message + the source code, or redirect users to the show_pyodide MCP App flow) and keep the current behavior only for "panel".

Copilot · 2026-03-06T18:27:17Z

+        if (payload.name) {
+          title.textContent = payload.name;
+        }
+        if (payload.description) {
+          description.textContent = payload.description;
+        }
+
+        const code = payload.code ?? "";
+        source.textContent = code || "No code provided.";
+
+        if (!code.trim()) {
+          runner.innerHTML = "";
+          return;
+        }


show_pyodide can return an error payload (e.g. when code is blank), but the renderer only looks at payload.code and otherwise shows “No code provided.”. This means users won’t see the actual error message in MCP App hosts. Consider rendering payload.error / payload.message when present so error states are visible.

Copilot · 2026-03-06T18:27:18Z

+
+**Use Case**: Standard display-server backed visualization flow with URL fallback behavior.
+
+**Returns**: Success/error message containing a view URL.


The show tool now returns a JSON text payload (as implemented in holoviz_mcp.server.display()), not a plain success/error message string. This “Returns” description is now misleading; update it to describe the JSON payload shape (and/or the fallback behavior in non-MCP-App hosts).

Suggested change

**Returns**: Success/error message containing a view URL.

**Returns**: JSON text payload (as returned by `holoviz_mcp.server.display()`) describing the view, including a view URL and rendering metadata. In non–MCP-App hosts, this may be surfaced to the user as a success/error message string containing the view URL.

Copilot · 2026-03-06T18:27:18Z

 When you use the `show` tool:

 1. AI sends code to the MCP server via the tool
 2. MCP server makes HTTP request to Display Server
 3. Display Server stores the snippet in SQLite database
 4. Display Server executes the code and captures output
 5. MCP server returns URL to view visualization
-6. User accesses visualization via URL in browser
+6. User accesses visualization via URL in browser (or via in-chat MCP App UI when supported)


This flow description still says the MCP server “returns URL to view visualization”, but show now returns a JSON payload (with url embedded) for MCP App rendering. Adjust the wording here to reflect the new contract, otherwise this doc contradicts the implementation and the show MCP App template logic.

Copilot · 2026-03-06T18:27:18Z

 The `show` MCP tool is the primary interface for creating visualizations. It accepts:

 - **app** (required): Python code to execute
 - **name** (optional): Human-readable title for the visualization
 - **description** (optional): Explanation of what the code does
- **method** (optional): Execution method - "jupyter" (default) or "panel"
+- **method** (optional): Execution method - "jupyter" (default), "panel", or "pyodide"


In the show tool section, the parameter name is documented as app, but the MCP tool parameter is code. Also, the surrounding text claims the tool returns id/created_at, but the current implementation returns a JSON payload with fields like status, message, url, and echoes code. Please update this section to match the actual show tool interface and payload.

Copilot · 2026-03-06T18:27:19Z

+@mcp.resource(
+    SHOW_RESOURCE_URI,
+    app=AppConfig(
+        csp=ResourceCSP(
+            resource_domains=[
+                "'unsafe-inline'",
+                "https://unpkg.com",
+            ],
+            frame_domains=[
+                "http://localhost",
+                "http://127.0.0.1",
+                "https://localhost",
+                "https://127.0.0.1",
+                "https://*.app.github.dev",
+                "https://*.github.dev",
+            ],


The show MCP App template embeds the visualization URL in an <iframe>, but the CSP frame_domains here only whitelists localhost and *.github.dev. When JUPYTER_SERVER_PROXY_URL / server.jupyter_server_proxy_url is set to a custom domain, _externalize_display_url() will return that domain and the iframe will likely be blocked by this CSP. Consider either (a) adding an allow-list entry for the configured proxy host, (b) relaxing frame_domains to a broader pattern (e.g. https:) if acceptable, or (c) not setting a restrictive frame_domains directive for this resource.

_internalize_url() converts externalized URLs (GitHub Codespaces port forwarding, Jupyter server proxy) back to localhost before Playwright opens them, so inspect_app() works correctly when panel-live-server externalizes the URL for the end user. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

MarcSkovMadsen added 4 commits February 28, 2026 18:53

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de64ee1

mcp apps

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Merge branch 'main' of https://github.com/MarcSkovMadsen/holoviz-mcp …

88ea500

…into enhancement/mcp-apps

mcp apps

477b6bc

Copilot AI review requested due to automatic review settings March 6, 2026 18:20

Copilot started reviewing on behalf of MarcSkovMadsen March 6, 2026 18:21 View session

Copilot AI reviewed Mar 6, 2026

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Enhancement/mcp apps#161

Enhancement/mcp apps#161
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		Use Case: Standard display-server backed visualization flow with URL fallback behavior.

		Returns: Success/error message containing a view URL.

	Returns: Success/error message containing a view URL.
	Returns: JSON text payload (as returned by `holoviz_mcp.server.display()`) describing the view, including a view URL and rendering metadata. In non–MCP-App hosts, this may be surfaced to the user as a success/error message string containing the view URL.

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